An 1884 cartoon by artist Frank Beard depicting Grover Cleveland's frustration at the Maria Crofts Halpin scandal.

Grover Cleveland is mostly known for being the only American president to serve two non-consecutive terms... not so much for being one of several possible fathers to an illegitimate son.
 

 Grover Cleveland in 1905

During his first campaign for the presidency in 1893, it was revealed by supporters of Republican James G. Blaine that Cleveland had paid child support to Maria Crofts Halpin. But things weren't as clear-cut as they seemed. Cleveland was one of several men who had been involved with Halpin, including Cleveland's friend and law partner Oscar Folsom.

No one knows who the real father of Oscar Folsom Cleveland was, but it's thought that Cleveland took responsibility because he was the only bachelor among them. Apparently Halpin really got around.

To add an extra layer of weirdness to the situation, Cleveland ended up marrying Oscar Folsom's 21-year-old daughter, Frances, 2 years after taking office in 1886. He was 49 at the time. This was not considered a scandal. One can only hope Folsom and Cleveland were clear on who fathered the girl.